As is known, an in-cylinder injection internal combustion engine using gasoline as fuel includes a high-pressure fuel pump that receives fuel pumped up from a fuel tank by a fuel pump, pressurizes the fuel to a pressure higher than the discharge pressure of the fuel pump, and sends the pressurized fuel to a delivery pipe (high-pressure piping) connected to an injector serving as a fuel injection device. Typically, in an internal combustion engine having such a high-pressure fuel pump, the pressure of fuel that has been pumped up from the fuel tank by the fuel pump is maintained at a “feed pressure”, which is not more than 400 kPa when the fuel is supplied to a fuel chamber formed in the high fuel pressure fuel pump. Fuel that has been supplied to the fuel chamber is then sent from the fuel chamber to a pressurizing chamber in a cylinder via an electromagnetic valve. When the amount of fuel in the pressurizing chamber is adjusted to a predetermined amount by an upward motion of a plunger vertically reciprocating in the cylinder, the electromagnetic valve is closed. When the electromagnetic valve is closed, the fuel is pressurized as the plunger is moved upward, and sent under pressure to the delivery pipe via a check valve. The pressure of fuel sent under pressure from the pressurizing chamber is variable between 4 to 13 MPa in accordance, for example, closing timing of the electromagnetic valve. Then, the fuel of which the pressure has been accumulated in the delivery pipe, is directly injected into the cylinders of the engine by valve opening of the injector. At this time, the amount of fuel that flows into the fuel chamber of the high-pressure fuel pump from the fuel pump per unit time is not necessarily equal to the amount of fuel that flows out from the fuel chamber to the pressurizing chamber in the cylinder per unit time. The difference in the fuel amount causes pulsations in the fuel pressure in the fuel chamber. Also, in such a high-pressure fuel pump, fuel that is being pressurized after being sent from the fuel chamber to the pressurizing chamber of the cylinder is returned to the fuel chamber, so that the amount of fuel sent from the pump to the delivery pipe is adjusted. Therefore, the pressure difference between the fuel in a section including the fuel chamber and the fuel that is being pressurized also generates pulsations of the fuel pressure in the fuel chamber. Such pressure pulsation of fuel, in other words, variation in pressure, varies the amount of fuel sent from the fuel chamber to the pressurizing chamber in the cylinder. This contributes to degradation of the adjustment accuracy of the amount of fuel sent from the high-pressure fuel pump to the delivery pipe.
Accordingly, high-pressure fuel pumps disclosed in Patent Documents 1 and 2 each have a pulsation damper that absorbs pressure pulsation of fuel in a fuel chamber, so as to reduce pressure pulsation described above.
The pulsation damper disclosed in Patent Document 1 has a cross-sectional structure shown in FIG. 9. That is, the pulsation damper has two sets of two diaphragms 71a, 71b provided in a fuel chamber 75 defined in a housing 70. The diaphragms 71a, 71b have outer peripheral joint sections 73a, 73b, which are welded to each other and supported by a support member 74. Each set of the diaphragms 71a, 71b has a gas chamber 72a, 72b between two diagrams. The gas chambers 72a, 72b are filled with inert gas of a predetermined pressure, for example, argon gas or nitrogen gas. The volume of the gas chambers 72a, 72b changes in accordance with the fuel pressure in the fuel chamber 75, so that pressure pulsation as described above is absorbed. The fuel chamber 75 receives fuel from a fuel tank (not shown) via a fuel passage 76 connected to the fuel chamber 75.
The pulsation damper disclosed in Patent Document 2 has a cross-sectional structure shown in FIG. 10 and includes a plate member 83 and a diaphragm 81. The plate member 83 forms a fuel chamber 85 with a housing 84. The plate member 83 and the diaphragm 81 are welded to each other at a joint section 81a at the periphery. An annular member 86 is provided along the joint section 81a. The plate member 83 is covered with a pump cover 80. A gas chamber 82 defined by the plate member 83 and the diaphragm 81 is filled with inert gas of a predetermined pressure, like the pulsation damper disclosed in Patent Document 1. In accordance with the fuel pressure in the fuel chamber 85, the diaphragm 81 is displaced into the fuel chamber 85 or toward the plate member 83, thereby absorbing pressure pulsation of fuel.
With either of the pulsation damper of Patent Document 1 or 2, when pressure pulsation of fuel occurs in the fuel chamber, the diaphragm is deformed in accordance with the pressure pulsation in a direction to increase or reduce the volume of the gas chamber. This absorbs the pressure pulsation, thereby reducing changes in the fuel pressure.
In either of these pulsation dampers, when the volume of the gas chamber changes due to deformation of the diaphragm, a force resulting from the pressure of gas filling the gas chamber acts on members forming the outer periphery of the gas chamber including the joint sections, that is, acts on the diaphragms and the plate member. The force acts from within the gas chamber toward the outside of the gas chamber. Thus, when the force acts on the joint sections, it acts to separate joined members, specifically, the joined diaphragms or the joined diaphragm and plate member. Such a force acts on the joint section each time the diaphragms are deformed due to pressure pulsation. Although the force does not completely separate the joined members from each other, the force causes delamination from the innermost parts of the joint sections. In other words, joint loosening occurs. Therefore, these pulsation dampers need to have members for preventing joint loosening such as the support member 74 (Patent Document 1) or the annular member 86 (Patent Document 2), which apply force for pressing joined members against each other.
Patent Document 1: Japanese Laid-Open Patent Publication No. 2008-19728
Patent Document 2: Japanese Laid-Open Patent Publication No. 2008-2361